Atomic numbers of a few elements are given here.
P-4, Q-10, R-11, S - 15, T - 17
Which of the following is correct regarding these elements?

Options

A. R and T will form a compound `R_2T`.
B. Q and S will combine to form `Q_5S`.
C. R and T both will form univalent ions.
D. P has complete octet in its L shell.

Answer

To determine the correct statements regarding the elements with atomic numbers P-4, Q-10, R-11, S-15, and T-17, we will analyze each element based on its electronic configuration and valence electrons.

### Step-by-Step Solution:

1. **Identify the Elements:**
- P (Atomic number 4) is Beryllium (Be).
- Q (Atomic number 10) is Neon (Ne).
- R (Atomic number 11) is Sodium (Na).
- S (Atomic number 15) is Phosphorus (P).
- T (Atomic number 17) is Chlorine (Cl).

2. **Determine the Electronic Configurations:**
- P (Be): 1s² 2s² (Total 4 electrons)
- Q (Ne): 1s² 2s² 2p⁶ (Total 10 electrons)
- R (Na): 1s² 2s² 2p⁶ 3s¹ (Total 11 electrons)
- S (P): 1s² 2s² 2p⁶ 3s² 3p³ (Total 15 electrons)
- T (Cl): 1s² 2s² 2p⁶ 3s² 3p⁵ (Total 17 electrons)

3. **Determine Valence Electrons:**
- P (Be): 2 valence electrons (2s²)
- Q (Ne): 8 valence electrons (2s² 2p⁶) - fully filled
- R (Na): 1 valence electron (3s¹)
- S (P): 5 valence electrons (3s² 3p³)
- T (Cl): 7 valence electrons (3s² 3p⁵)

4. **Analyze Reactivity and Compound Formation:**
- R (Na) can lose 1 electron to form a univalent ion (Na⁺).
- T (Cl) can gain 1 electron to form a univalent ion (Cl⁻).
- Therefore, R and T can form a compound (NaCl).

5. **Check Statements:**
- **Statement 1:** R and T form a compound. **True** (NaCl).
- **Statement 2:** Q (Ne) is inert and does not form compounds. **True** (Neon has a complete octet).
- **Statement 3:** R and T are univalent ions. **True** (Na⁺ and Cl⁻).
- **Statement 4:** P has a complete octet in its L-shell. **False** (P has only 4 electrons; L-shell can hold a maximum of 8).

### Conclusion:
The correct statements regarding these elements are:
- R and T can form a compound.
- Q is inert and does not form compounds.
- R and T can form univalent ions.